tdd-workflow

TDD Workflow Skill — Test-First Development

This skill enforces a strict Test-Driven Development workflow ensuring every line of production code is justified by a failing test.

The TDD Cycle

┌─────────────────────────────────────────────┐
│                                             │
│   ┌─────────┐    ┌─────────┐    ┌────────┐ │
│   │  RED    │───▶│  GREEN  │───▶│REFACTOR│ │
│   │Write    │    │Make it  │    │Clean it│ │
│   │Failing  │    │Pass     │    │Up      │ │
│   └─────────┘    └─────────┘    └────────┘ │
│        │                              │     │
│        └──────────────────────────────┘     │
│                  REPEAT                     │
└─────────────────────────────────────────────┘

Test Categories

Unit Tests (Foundation)

• Test a single function/method in isolation
• Mock all external dependencies
• Fast (< 10ms per test)
• No file system, network, or database access

describe('calculateTotal', () => {
  it('should sum all item prices', () => {
    const items = [{ price: 10 }, { price: 20 }, { price: 30 }];
    expect(calculateTotal(items)).toBe(60);
  });

  it('should return 0 for empty array', () => {
    expect(calculateTotal([])).toBe(0);
  });

  it('should handle negative prices with absolute value', () => {
    const items = [{ price: -10 }];
    expect(calculateTotal(items)).toBe(10);
  });
});

Integration Tests (Service Boundaries)

• Test interaction between modules
• Use real implementations where possible
• Use test databases/containers for data layer
• Verify contracts between services

E2E Tests (User Journeys)

• Test complete user workflows
• Run against real environment
• Minimal mocking
• Focus on critical paths

What to Test

For Every Function

Category	Test Cases
Happy Path	Normal inputs → expected outputs
Boundaries	Empty, single, max, min values
Null/Undefined	Missing optional parameters
Type Errors	Wrong input types
Error Conditions	Expected failures
Concurrency	Race conditions if applicable